High Dynamic Range Images (HDR)

Since the last camera upgrade last year (details here), I've been experimenting with the HDR techniques. My previous cameras did not have the exposure auto-bracketing function, and this function was one of the reasons why I have decided to buy a Canon 450D.

HDR comes from Higy Dynamic Range images and refers to images having a greater dynamic range of luminance between the light and darker part of a scene than normal photography techniques. Its intention is to more accurately render the wide range of light intensity levels found in real scenes (from direct sunlight to shadows for example). Although most of the time over-processing that looks fake is associated with this technique, its scope is to render an image closer to how it is perceived by our eyes.

This technique was first developed around 1930s and 1940s, but the first applications in digital photography appeared in 1993. A HDR image can be considered even the raw file of the most recent digital cameras, as one pixel is defined in 24 bits (having thus a wider range of luminance), but on its display on the screens (camera and computer screens) it looses information as the pixel-depth is only 8 bits. Tone-mapping techniques have been introduced to convert a 24 bits image to 8 bits, in an attempt to differentially map the luminance levels of each pixel. Different algorithms are available on the market to make this conversion, the most notable being the one included in the most recent Photoshop releases or from the specialized software for HDR - Photomatix.

The tone-mapping technique can be apply to a raw image or at least 2 jpeg images of the same scene taken with different exposures, with comparable results. Many parameters of this technique influence the final result. The following results can be noted: details in both shadows and direct sunlight or both the sky and subject and enhanced color rendering.

To create my own HDR images I take 3 shots of the same scene with different exposures (bracketing +/-(1+1/4) usually). I use the tone-mapping algorithm from Photomatix and set the parameters so that the final results to look as real as possible. However, the images obtained this way look different than normal exposed photographs.

Just before Christmas, the first serious snow provided an opportunity for a photo trip in the surroundings. We have reached the Castle of Aigle a little too early in the morning and half of the Castle was still in shadow. The normal approach to photograph it would render the shadow part almost completely dark, given the bright sunshine and the white caps of the mountains in the background. By using tone-mapping technique, detail of the dry vineyards in the foreground were able to be preserved, generating an image similar with the one perceived by my eyes.

This HDR render of the Rathaus (city-hall) in Vienna did not bring almost anything extra to the image taken with normal exposure other than slightly increased color saturation without altering the quality.

The image on the right taken in the Unirii Square in central Timisoara, Romania is however totally different than the normally exposed one. The thin layer of clouds are causing a uniform light which the normal capturing technique cannot render properly. The sky ended up almost completely white, while the details and colors of the buildings were washed out by under-exposure. I couldn't believe my eyes when the algorithm generated this image - beautiful details in the sky; warm colors of the buildings and even a pure and bright green of the meadow... It was one of the best surprised that HDR has yet offered me...

Another magnificent example of the HDR technique with tone-mapping is this picture taken in Lausanne, Switzerland. Amazing details have been obtain in the area under the bridge and rooftops in the foreground, while the Notre-Dame of Lausanne cathedral shines as a crown over the city in front of a gloomy dark sky.

This last picture of Ouchy Castle in the port of Lausanne on Lake Geneva, Switzerland is not exactly what I was hopping for. From my previous experience with overcast skies I was hopping to obtain more colors in this composition. However the gloomy result has its own charm...

I am continuing to experiment with HDR techniques. Some more images are even on the pending line... Let me direct you to a personal gallery of HDR images, where my further experiments will be found.

Lieska:I do not have any problems with noise. I believe that noise appears when you set the parameters to unrealistic values, providing that the original photos are noise-free. Try to keep the saturation to average values and do not clip too much from from the whites and the blacks (check the histogram while you do this). If you do not obtain a proper histogram, try re-shooting with different exposure correction. There are also parameters noise-filters with which you can play. My only concern is that some pictures end up too soft, but I believe to be the problem caused either by my lens (kit lens which I am hopping to upgrade any time soon) or the tripod which seem not to stable...

To all:Thanks for the compliments. I am also eager to find out the result of your experiments...

good pictures!I recently focus on HDR making, but I'm really not good at it.maybe the pictures I chose has too large difference on exposure. hope we could do better.btw, I tried photomatix, it generate too much noise and cannot be used at all, what ever with NEF or JPGs. :(

I use ReDynaMix HDR 1.01. This plug-in for Photoshop allows you to make HDRimage using only 1 image. Yes, it is pseudo effect, but the results are very interesting! As for the monitor or on paper. Believe me! The choice of image processing depends on how you will use this picture. For artistic purposes quite fit this plug. But for 3D rendering (HDRi maps) make better use of the technique described by the author.))

Littledesire - may I suggest downloading easyhdr. If you want to register is about $40 or so. Load that one raw file - and then do an LDR (low dynamic range) enhancement. I think you'll like the results. True HDR needs 3 shots. Usually -2, 0, +2 on the exposure. You can't save one file as you described - but you can do ldr with that one image - at least with easyhdr.

Littledesire:I am using jpeg images for the moment, but 3 jpeg images with different exposure taken with the camera, not exported from raw (you need a tripod and a camera which has a function for auto-bracketing - most new models do, even P&S). As far as I understand 1 raw file cannot properly generate the details in the shadows, so in-camera you need to over-expose the shot. Maybe photomatix (you can download a trial version on-line for testing) will be able to generate the image for you, but it will anyhow be of low quality (a lot of noise). I could also suggest to try with +/- 1 exposure correction instead of +/-2. Let me know any results... I have many experiments to make myself...

Davidwattsjr:There are some very nice ones! Thank you for pointing them out... I found it difficult to anticipate the time when HDR will bring a plus to the normally exposed shot. I believe is more or less like shooting on film: you don't know the results until you process them...

I've been experimenting quite a bit with this for the past year or so... I personally use easyhdr (www.easyhdr.com) and have found it to be quite effective. Several shots of mine on Dreamstime are processed this way.

Nice blog!Yhca, in Photoshop go to File>Automate>Merge to HDR and that's it!

But I have some problem. Bogdan, I'm really interested in HDR and I'm trying for 1 month to create one! I've read all the blogs and forums but there something wrong with my try. So, here it is: I use 1 RAW file (Nikon) and save it 1. normal, 2. +2 exposure and 3. -2 exposure. And when I try to merge them in HDR, accures a sign: "There is not enough dinamic range in these photos to construct a useful HDR image".Do you merge raw files or jpg? I tried both but ... nothing.Can someone help me? Or maybe I should try Photomatrix

I use Photomatix software. I have also tried with Photoshop, but the results were not so good. I believe there are other similar softwares as well... Just google it... On the link presented above, there is also a comprehensive explanation of HDR merging technique.

High, I tried this method but I do not know how to merge them 3 together in Photoshop. It gives a diagonal dark and bright separation lines across the merged photos. How do you merge them together? In Photoshop?

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